Rigid PVC compounding compositions exhibiting weather resistance and PVC degradation resistance in hot sunny climates

ABSTRACT

Rigid PVC resins are compounded with a chalk-like Caribbean micritic calcium carbonate to provide improved weathering resistance of rigid PVC articles subjected to external exposures of heat and sunlight. The effective resistance to heat and sunlight is substantially increased by rigid PVC resins compounded with European chalk and Caribbean micritic calcium carbonate, zinc dialkyl ester scavenger and organotin stabilizer to provide considerably increased PVC degradation resistance.

[0001] This invention pertains to polyvinyl chloride (PVC) and more particularly to weather and heat resistant rigid PVCs used externally and exposed to harsh environmental conditions of excessive heat and sun common in southern exposures.

BACKGROUND OF THE INVENTION

[0002] Rigid PVCs contain little or no plasticizer and are commonly used in a wide variety of internal uses sheltered from direct outside environmental exposure. Rigid PVCs are known to degrade upon exposure to sunlight, heat and UV, which degrades the polymeric structure of PVCs and generates trapped HCl acid. To have any practical commercial use in outdoor environments, products made from rigid PVCs, such as house siding, door and window profiles, shutters, roof vents and sashes, outdoor fencing and decking, and similar exterior applications, the PVC polymeric structures must be stable and resistant to heat and sunlight. Colors for rigid or semi-rigid PVCs, if used externally, are typically limited to white and light pastel colors due to color fade and deterioration.

[0003] Heat and sunlight degrade the polymeric structure of PVC by generating HCl acid trapped in the rigid polymeric structures where formation of HCl is catalytic and in turn accelerates further degradation and further generation of HCl acid along with additional degradation. The tendency to decompose is accelerated at elevated temperatures and direct sun exposure or by catalytic materials such as traces of iron or zinc compounds. Zinc compounds such as zinc acetate are known to react with PVCs to cause dechlorination and similarly can react with tin compounds to form detrimental zinc chloride. In harsh environments, particularly hot and dry sunny climates, the sun and heat cause a considerably increased rate of degradation of the PVC polymeric structure. Dark colors are more prone to absorb heat and further increases instability and degradation of PVCs. Consequently, the exposed plastic materials made of rigid PVCs rapidly discolor, frequently become brittle, and otherwise crack and deteriorate.

[0004] According to J. of Vinyl Technology, September, 1983, vol. 5, No. 3, pages 91-95, degradation of PVC by exposure to heat and sunlight is known to cause degradation of the PVC polymeric structure wherein UV light imparts sufficient energy to break PVC chemical bonds, while visible light causes color discoloration, and near infrared light contributes to heat degradation and poor weatherability. PVC degradation generates HCl while causing double bond formation in the PVC polymeric structure. PVC physical deterioration absorbs light causing poor weathering resistance including yellowing and oxidation bleaching. Oxidized PVC becomes water sensitive causing surface erosion, brittleness and cracking, according to the journal article. Such PVC polymeric degradation is especially critical in rigid PVCs substantially free of plasticizers.

[0005] In contrast, semi-rigid or flexible PVCs containing appreciable amounts of plasticizer do not tend to degrade and thus are used for exterior moldings and extrusions for trim and siding of buildings exposed to outside environments. The degradation is particularly sever in rigid PVCs with no plasticizer, while semi-rigid or flexible PVCs containing appreciable levels of plasticizer provide a porosity in the plastic structure and facilitate expulsion of HCl acid formation, which in turn minimizes the sunlight and heat degradation. Similarly, foamed PVC plastic materials are inherently porous and provide a means for expulsion of HCl acid that may be generated and otherwise retained. Semi-rigid PVCs ordinarily contain above about 10 weight parts external plasticizer, while flexible PVCs ordinarily contain more than about 25 weight parts, both based on 100 weight parts of PVC resin. Since plasticized PVCs are more resistant to heat and sunlight, rigid PVCs ordinarily are not used in external exposures, especially in harsh hot and sunny climates, due to the inherent degradation of rigid PVCs and inherent characteristic of retaining acid generated on exposure to heat and sun.

[0006] Stabilizers are known to reduce the adverse weathering effects of exposure to heat and sun and are frequently added to PVCs used externally. Alkaline materials such as barium oxide or sodium silicate or certain organometalic materials of tin or lead can stabilize PVCs by removing traces of HCl chemically as the HCl forms and thereby eliminate HCl degeneration as well as the catalytic effect of HCL acid generation. The stabilizers are known as heat stabilizers and can include alkaline oxides, hydroxide carbonates, amines, lead salts, sodium silicate, barium-cadmium soaps, and dibutyl tin dilaurates. To obtain maximum effectiveness, a mixture of stabilizers frequently is utilized, where one stabilizer may be effective against heat, while another may be effective against sunlight. Such stabilizer combinations are helpful in semi-rigid or flexible PVCs, but are only marginally helpful in compounding rigid PVCs. However, rigid structures are preferred for most structural applications due to structural integrity and durability such as impact resistance.

[0007] Calcium carbonates are commonly used as filler materials in PVCs, but are not known to provide weather resistance or resistance to polymeric degradation upon exposure to heat and sunlight. In the United States, calcium carbonates are based on limestone or marble deposits. Commercial grades ordinarily are processed precipitated calcium carbonates and typically contain perceptible levels of iron of trace amounts above about 200 ppm iron which can activate HCl generation in PVCs. In England and Europe, calcium carbonates are primarily chalky ore deposits. Caribbean calcium carbonates described as micritic chalk-like, marine based and sedimentary in origin are disclosed in U.S. Pat. No. 5,102,465 for use as filler material in polyester molding compounds.

SUMMARY OF THE INVENTION

[0008] It now has been found that certain chalk-like marine calcium carbonates known as Caribbean micritic calcium carbonates derived from soft friable marine fossil sedimentary deposits are especially useful in rigid PVCs and surprisingly function as a scavenger for free HCl acid generated in PVCs to provide considerable weathering resistance, in addition to contributing an inexpensive source of filler material to the compounding of the rigid PVCs. It has been further found that a combination of limited amounts of a lower dialkyl acid ester of zinc scavenger, especially zinc octoate, and an organotin acid stabilizer together provide especially improved degradation resistance in combination with the Caribbean calcium carbonate, which collectively provide considerably improved degradation resistance when subjected to hot and sunny exposures. The Caribbean calcium carbonate surprisingly exhibits HCl scavenger properties and contributes to neutralization or absorption of HCl to eliminate HCl acid evolving upon heat and sunlight exposure degradation. The Caribbean calcium carbonate is an effective scavenger by itself, but is especially effective in conjunction with low levels of zinc dialkyl ester scavenger and organotin stabilizer, where the HCl scavenger effectiveness is increased considerably with increased levels of Caribbean calcium carbonate. Low levels of zinc dialkyl ester likewise function as an HCl scavenger without degrading the polymeric structure of PVCs to provide weathering resistance, eliminates any sulfur generated by tin mercaptide stabilizers, and surprisingly does not adversely interact with the organotin stabilizer.

[0009] In accordance with this invention, extruded or molded rigid PVCs can be particularly utilized for exterior exposures in hot and sunny environments utilizing rigid PVCs to form plastic components for external use. The rigid PVCs exhibit substantially improved resistance to acid generation, acid degradation, discoloration, cracking and other weathering physical deterioration of PVCs due to excessive heat and sun exposure. Enhanced color retention and stability can be achieved with white pigmented PVCs, along with pastels and medium depth pigmented colors, as well as with darker colors. These and other advantages of the invention will become more apparent by reference to the detailed description and the illustrative examples hereinafter.

[0010] Briefly, the invention comprises rigid PVCs utilized for extrusion, molding or other formation of rigid plastic components utilized particularly for external exposures to heat and sunlight. The rigid PVC compounded compositions contain at least about 2 weight parts of Caribbean micritic calcium carbonate based on 100 weight parts PVC resin to scavenger and prevent the generation and autocatalytic acceleration of HCl acid. The scavenger characteristics of the Caribbean calcium carbonate are enhanced considerably by compounding PVC with the combination of at least about 0.1 weight parts of a lower dialkyl ester of zinc scavenger, preferably a zinc octoate, and at least about 0.5 weight parts of an organotin heat stabilizer, preferably a dibutyl tin mercaptide, both weight parts based on 100 weight parts of PVC.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The invention is based on rigid PVCs for exterior exposure containing Caribbean micritic calcium carbonate as an HCl acid scavenger and optionally enhanced with a zinc organic dialky ester scavenger in conjunction with an organotin stabilizer

[0012] Referring first to the micritic calcium carbonate, Caribbean calcium carbonates are distinguished from calcium carbonates mined from limestone or marble ore deposits in the United States or chalk deposits in England or Europe in that the Caribbean calcium carbonates are mined from soft and friable, finely divided, chalk-lines marine sedimentary deposits frequently occurring as surface deposits in the Caribbean area. Caribbean calcium carbonates are high purity, finely divided, fine particle size friable deposits described as Caribbean micritic limestone in U.S. Pat. No. 5,102,465, hereby fully incorporated by reference, and sedimentary in origin comprising a combination of reef limestone deposits of reef fossil fragments, betrital deposits of fibrous skeletal and non-skeletal grains, micrite deposits of naturally formed precipitated calcium carbonate in beds or matrix with betrital, and chalk deposits of disarticulated caccolith fragments. Caribbean micritic calcium carbonates are soft and friable, chalk-like consistency, sedimentary deposits comprising reefs, betritals, micrite and chalky deposits. Caribbean calcium carbonate deposits tend to agglomerate in the natural sedimentary state but can be readily broken down or commutated to produce rounded porous particles comparable to naturally occurring particles less than about 6 microns. Useful Caribbean calcium carbonates have a particle size less than about 10 microns, desirably about 6 microns or less, preferably having a typical particle size distribution of about 70% less than about 3 microns, where particles from about 1 to about 3 microns or lower are most preferred. Smaller particles increase the surface area and in turn increases the scavenger effectiveness against PVC degradation. Caribbean micritic calcium carbonates are found throughout the Caribbean basin with significant deposits found in Haiti and Jamaica. Caribbean micritic calcium carbonates, especially Jamaican origin, are very high in purity typically exhibiting above 98% and typically more than about 99% pure calcium carbonate, with minimal amounts of impurities. Both wet ground and dry ground Caribbean calcium carbonates are effective for eliminating free HCl acid generation in PVCs, although water ground is preferred and has been found to be more effective. In contrast, chemically processed precipitated Caribbean micritic calcium carbonates are not effective HCl scavengers nor prevent PVC degradation in accordance with this invention. Accordingly, non-precipitated Caribbean calcium carbonates excludes those Caribbean deposits chemically processed to form precipitated calcium carbonates.

[0013] Jamaican micritic calcium carbonate is preferred and characteristically contains high purity calcium carbonate, typically more than about 99% by weight pure calcium carbonate, and commonly mined from surface sedimentary chalky marine deposits of friable fragile agglomerated particles. The deposits can be subsequently wet or dry ground by grinding for instance by a hammer mill followed by ball mill grinding to obtain the small particle size. Useful Jamaican micritic calcium carbonates are obtained directly by grinding without using a chemical precipitation processing commonly used in the U.S. with U.S. limestone and marble deposits. U.S. deposits also typically contain perceptible levels of iron which can promote discoloration and degradation of PVCs. In contrast, Caribbean and Jamaican micritic calcium carbonates are free of measureable amounts of iron. Preferred Jamaican calcium carbonate particles are approximately six microns or less in particle size. At about six microns or below, the ground calcium carbonate particles are hydrophobic and become more effective with decreasing particle sizes. Most preferred particles sizes are about predominately about 3 microns or below for protecting rigid PVCs in accordance with this invention, while particles less than about 1.5 microns are best. Purity of the ground particles on a weight basis ordinarily is above about 99%, typically above about 99.3% pure calcium carbonate, essentially free of iron (that is less than about 0.5% or less than about 0.2%, or nil), and with minimal impurities of less than about 1.0% or about 0.4% magnesium carbonate, less than about 0.1% crystalline silicates, and less than about 0.3%, acid insolubles, if any. Preferred useful commercial Jamaican calcium carbonates are Optifil and Optifil T calcium carbonates supplied by J. B. Huber Co. and described as 99% pure, virtually free of crystalline silica and other impurities such as magnesium carbonate and silicates, and free of other metals such as iron. Optfil T is preferred and is surface treated with stearate. Published physical properties of Optifil and Optifil T calcium carbonates from Jamaica are as follows. Grind (Hegman) 6 microns Oil absorption 1.7 lbs/100 lbs (Optifil) 1.6 lbs/100 lbs (Optifil T) Moisture 0.2% Specific surface area 3.45 m²/gm Calcium carbonate 99% Magnesium carbonate 0.4% Crystalline silica 0.1% maximum Silicates 0.2% maximum

[0014] In accordance with this invention, at least about 2 weights parts of Caribbean calcium carbonate, advantageously between about 2 and about 50 weight parts, and preferably between about 5 and about 15 weight parts are compounded with 100 weight parts of rigid PVC resin to obtain desired effective results of using Caribbean calcium carbonate in this invention. Higher levels and smaller particles of Caribbean calcium carbonate provide increased effectiveness as an HCl scavenger.

[0015] In a preferred aspect of this invention, Caribbean calcium carbonate is utilized in conjunction with an organotin heat stabilizer to further enhance the effective resistance to HCl acid generation in PVCs. Useful organotin stabilizers are mono-, di-, or tri-substituted alkyl or alkyl esters of tin known as alkyltins, where the remaining valences of the alkyltins are activated mono-, di-, or tri-substituted active mercapto groups (mercaptoacids and their esters, or mercaptides), or active carboxylic acids and their esters known as carboxylates (e.g. maleic or lauric acids, or maleic esters or half esters) such as dibutyl tin carboxylates. Active mercapto tin compounds ordinarily are referred to as thiotins, while active carboxylic acid or esters of tin are known as carboxylates. Organotins are excellent heat stabilizers and considerably enhance the short and long term stability of PVCs containing Caribbean calcium carbonate in accordance with this invention. The effectiveness of the organotins is primarily influenced by the non-alkyl activated mono-, di-, or tri-substituted mercapto groups or carboxylate groups, where thiotins and especially dialkythiotins are preferred. Preferred alkyltin stabilizers contain reactive mercapto ligands substitutions in thioglycolates (mercaptide) and/or reverse mercaptide esters. Preferred stabilizers are metallic tin salts of organic acid comprising tin dialkyl ester mercaptides. Useful organotin mercaptide ester stabilizers comprise alkyl tins including methyl tins, butyl tins, reverse ester tins, octyl tins, and tin corboxylates, where dibutyl tin mercaptides are preferred, and the most preferred is dibutyl tin ethyl hexyl mercaptoacetate. A commercially preferred organotin stabilizer is Thermolite T-31 sold by Atochem and described as dibutyl tin ethyl hexyl mercaptoacetate. The organotin stabilizers effectively prevent or counteract HCl generated in PVCs by heat and sunlight exposure and avoid degradation of PVC polymers. Organotin stabilizers are believed to deactivate labile chlorine atoms in the PVC chain by replacement by the ligand groups of the stabilizer, and/or bind HCl evolved in incipient degradation, and/or reaction with double bonds of polyene sequences, and/or scavenging of free radicals, and/or decomposition of peroxide groups forming due to PVC decomposition. At least about 0.5 weight part, desirably from about 0.5 to about 3 weight parts, and preferably from about 1 to about 1.5 or about 2 weight parts of organotin stabilizer are used with 100 weight parts PVC resin.

[0016] In a preferred aspect of this invention, Caribbean micritic calcium carbonate is utilized in conjunction with an organotin stabilizer and optionally in combination with limited amounts of a dialkyl ester scavenger. Useful organic scavengers comprise dialkyl organic esters of zinc comprising zinc metal reacted with a lower aliphatic alkyl mono-caroxylic acid having from about 4 to about 12 carbon atoms, preferably a lower fatty acid having from about 6 to about 10 carbon atoms, where about 7 to about 9 carbon atoms are most preferred. Useful preferred alkyl ester groups include hexyl, septyl, octyl, nonyl, and decyl esters, where the dialkyl ester groups can be the same or different alkyl chains. The most preferred alkyl is octyl and zinc octoate is the most preferred commercial zinc octoate is L 230 sold by Baerlocher U.S.A. located in Dover, Ohio. Zinc alkyl esters interact with the organotin compound to prevent PVC degradation but surprisingly do not form zinc chloride, a known PVC destabilizer, provided the equivalents of zinc do not exceed the active equivalents of non-alkyl mercapto or carboxylate components in the organotin stabilizer. The limited levels of zinc dialkyl ester combined with excess organotin considerably increase the effectiveness of the Caribbean micritic calcium carbonate and provides considerable weather and degradation resistance in accordance with this invention. The zinc dialkyl ester scavenger is limited relative to the amount of organotin in that the non-alkyl active ligand comprising mercapto or carboxylate groups exceed the equivalent alkyl content in the zinc dialkyl ester. A deficiency of mercapto or carboxylate equivalent relative to excess zinc has been found to generate free zinc and will cause detrimental zinc deterioration of PVC and formation of undesirable zinc chloride. Conversely, excess equivalents of mercapto or carboxylate groups available to complex with lesser equivalents of zinc avoids free zinc and avoids zinc deterioration of PVC. With higher substituted organotins, such as tri-functional mecapto groups, the ratio of tin to zinc can be as low as 0.75 to about 1, while di-functional substituted active groups, such as di-mercapto groups, the equivalent tin to zinc ratio is from about 10 to about 5.0, where the preferred ratio is from about 1.5 to 3. Similarly, mono-substituted mercapto organotins will be higher to provide sufficient mercapto groups to complex with less zinc dialkyl ester. Excess organotin equivalents relative to deficient zinc ester equivalents have been found to increase the overall efficiency for precluding and avoiding PVC degradation. On a weight basis, PVC resin is compounded with zinc dialkyl ester at a level above about 0.1 weight part, usefully from about 0.1 to about 3 weight parts or more depending on the active non-alkyl active ligand group in the organotin, preferably from about 0.1 to about 2 weight parts, where the most preferred levels are from about 0.5 to about 1 weight parts, based on 100 weight parts of PVC resin.

[0017] Other supplementary additional stabilizers can be added if desired. Lead salt stabilizers are useful and further enhance weather resistance where lead reacts with and neutralizes nascent HCl generated to form an inert lead chloride which remains stable and non-autocatalytic. Lead chloride does not promote degradation of rigid PVC polymers, although performance of lead stabilizers may be diminished in the presence of other co-stabilizers other than cadmium/barium stabilizers. Other useful stabilizers include alkaline materials such as barium oxide or sodium silicate for providing weather resistance. Useful heat stabilizers include alkaline hydroxides, hydroxide carbonates, amines, sodium silicate, and barium cadmium soaps. To obtain maximum effectiveness, a mixture of stabilizers can be used where one stabilizer may be effective against heat while another may be effective against sunlight. The foregoing stabilizers can be used in conjunction with the organotin stabilizer, if desired. Another useful stabilizer is a calcium zinc compound where calcium forms harmless calcium chloride and avoid formation of detrimental zinc chloride.

[0018] In a less preferred aspect of this invention, some European (including England) calcium carbonates comprise naturally occurring chalk ore deposits useful in this invention in conjunction with an organotin stabilizer and limited amounts of zinc alkyl ester scavenger to provide enhanced resistance to heat, sunlight and weathering degradation of rigid PVCs. Chalk is a soft amorphous calcium carbonate formed by fossil shells known as coccolith shells. Chalk calcium carbonates differ in origin from limestone and marble found in North America in that chalk origin comprises shells of coccolith organisms. In this aspect of the invention, European naturally occurring chalk calcium carbonates can be milled to micron size particles less than about 10 microns, preferably less than about 5 microns, and most preferably from about 1 to 3 about microns, or less, which exhibit improved heat and weather resistance to PVC degradation in conjunction with the combination of organotin stabilizer and limited amounts of zinc alkyl ester scavenger. Useful European chalk calcium carbonates are non-precipitated friable chalk deposits inasmuch as chemically processed precipitated European calcium carbonates are ineffective and do not impart any reduction in heat or weathering degradation in rigid PVCs. Unlike Caribbean micritic calcium carbonate, European non-precipitated chalk calcium carbonate alone does not provide significant resistance to PVC degradation. Accordingly, in this aspect of the invention, non-precipitated chalky European calcium carbonate particles in conjunction with the combination of organotin stabilizer and limited levels of zinc alkyl ester scavenger considerably improves resistance to HCl generation and further enhances HCl scavenger characteristics. The levels of European calcium carbonate useful in PVC resin compounding are comparable to Caribbean micritic calcium carbonate as well as useful levels of organotins and zinc alkyl esters previously described, provided the reactive equivalents of zinc are less than the non-alkyl activated ligand equivalents on the organotin to assure a deficiency of zinc relative to excess equivalents of active ligands to complex with deficient zinc.

[0019] Rigid PVCs utilized in this invention comprise PVC being essentially a homopolymer with minimal amounts of less than about 5% by weight copolymerized other vinyl comonomer, but preferably little or no copolymerized other vinyl monomer. Commercial PVC ordinarily comprises about 56% by weight chlorine. Poly (vinyl chloride) comprises polymerized vinyl chloride monomer where preferred PVC polymers are essentially homopolymerized vinyl chloride with little or no copolymerized other vinyl co-monomers. Preferred PVCs are essentially homopolymers of polymerized vinyl chloride. Useful vinyl co-monomers if desired include vinyl acetate, vinyl alcohol, vinyl acetals, vinyl ethers, and vinylidene chloride. Other useful co-monomers comprise mono-ethylenically unsaturated monomers and include acrylics such as lower alkyl acrylates or methacrylates, acrylic and methacrylic acids, lower alkyl olefins, vinyl aromatics such as styrene and styrene derivatives, and vinyl esters. Useful commercial co-monomers include acrylonitrile, 2-hexyl acrylate, and vinylidene chloride. Although co-monomers are not preferred, useful PVC copolymers can contain about 0.1% to about 5% by weight copolymerized co-monomer, if desired.

[0020] Preferred PVCs are suspension polymerized vinyl chloride monomer, although mass (bulk) polymerized polymers can be useful, but are less preferred. Rigid PVCs contain little or no plasticizer, and, if present, ordinarily no more than about 5 weight parts placticizer per 100 weight parts of PVCs. The PVCs of this invention have an inherent viscosity from about 0.45 to about 1.5, preferably from about 0.5 to about 1.2, as measured by ASTM D 1243 using 0.2 grams of resin in a 100 ml of cyclohexanone at 30 degrees C.

[0021] In compounding the rigid PVCs, other compounding components are desirably incorporated into the PVC resins to form compounded PVCs useful for forming extrusion or molded components used in exterior environments. In addition to heat stabilizers, other compounding ingredients can include fillers, pigments and colorants, processing lubricants, impact modifiers, other processing aids, as well as other additives if desired, such as biocides and flame retardants. Fillers ordinarily are used to reduce cost and gloss and can include conventional calcium carbonates derived from limestone or marble but ordinarily will not be used in this invention with the Caribbean micritic calcium carbonate. Other fillers include clay, talc, mica, and diatomaceous earth fillers. Useful pigments and colorants can be organic, but preferably inorganic mineral, such as titanium dioxide for opacity and UV absorption. Processing lubricants can be external lubricants to reduce sticking to hot processing metal surfaces and can include low molecular weight polyethylene, paraffin oils, and paraffin waxes. Internal lubricants increase flow of resin particles within the resin melt and can include metal stearates such as stearic acid. Impact modifiers are useful in rigid PVCs to increase toughness and can include chlorinated polyethylenes, ABS polybutadiene, acrylic or methacylic polymers or copolymers, or butadiene-styrene (MBS). Other processing aids for extruding rigid PVCs in complex profiles include acrylic or styrene-acrylonitrile copolymers to prevent edge tear in the extrusion of complex profiles.

[0022] In compounding the rigid PVCs, the PVC resin is mixed with the various other compounding ingredients in low shear mixers such as a paddle or ribbon blender, although high shear mixers ordinarily are preferred. Useful mixers include a Ross Planetary mixer, a Henshel mixer, Hobart mixers, Banbury mixer, and a Henshel mixer and ribbon blender. In high speed mixing, heat is typically generated while mixing. The compounded PVCs are then cooled to avoid thermal degradation and thereafter can be stored for later use. Compounded rigid PVCs typically are extruded to form pellets or other solid particles useful in molding or extruding operations to produce rigid plastic components, such as sheets for roofing and wall panels, cladding, house siding, window frames, linear trim and similar exterior uses. Similarly, rigid PVC can be extruded or molded as cap stock fused or otherwise adhered to substrate plastics other than rigid PVC. Co-extruded or laminated cap stock can be prepared as shown in U.S. Pat. No. 4,100,325 to form a composite layer or laminated plastic article. Co-extrusion comprises extrusion of two or more polymeric layers simultaneously brought together into contact at a point prior to extrusion through a shape forming co-extrusion die such as shown in U.S. Pat. No. 3,476,627.

[0023] An important accelerated test for measuring resistance to heat, sunlight, and UV radiation, and particularly measuring color changes due to the accelerated exposures, is the QUV weather tester manufactured by Q-Panel Company, which uses UV-B lamps with an energy peak at 313 mm. The QUV accelerated weathering cycle is about 20 hours of light exposure at 50 degrees C., followed by about 4 hours darkness with condensation at 40 degrees C. Color changes are measured by delta E calculated by the Friele-McAdams-Chickering equations as found in Journal of the Optical Society of America, 58, 290 (1960) authored by G. Wyszeck.

[0024] The merits of the invention are further illustrated and exemplified by the following examples.

EXAMPLES 1 TO 14

[0025] The following raw materials were compounded into rigid PVC resin to form experimental compositions Examples 1-14 at a constant weight parts level indicated as follows. WEIGHT COMPONENT MATERIAL DESCRIPTION PARTS a. SE 950 EG PVC of 0.9 inherent viscosity 100 b. T-31 (S008) Dibutyl tin ethyl hexyl mercaptoacetate 1 c. Baerostab L230 Zinc octoate 0.5 d. Calcium stearate Calcium stearate 1.25 e. Loxiol G33 Mixture ester fatty acids/alcohols 0.25 f. Paraffin 165F Paraffin wax 0.65 g. EBS wax powder Ethylene bis-steramide 0.5 h. Paraloid K120N Methacrylate processing aid 1 i. Kronos 2160 TiO₂ durable grade 10 j. Paraloid K175 Acrylic lubricant processing aid 1 k. Filler CaCO₃ indicated in Table Variable

[0026] Using the above components as a basic mixture for all experimental samples compounded, variable filler additives indicated in the table below were added to form individual compositions for Examples 1 to 14 inclusive below.

[0027] Filler Information C. E. B. Optifil Camel F. Brand A. Optifil JS D. Cal Polar Name Optifil T 100T (W1T) Omyalite ST 8101C Ore Type Chalk Chalk Chalk Chalk Lime- Chalk stone Country Jamaica Jamaica Jamaica France USA Jamaica Origin Mfg. Dry Dry Wet Wet Wet Precipit. Process Dry Y 93 93.9 96 brightness Mean 1.5 1.3 1.2 0.7 particle size (microns) % less 50% than 2 microns % less 19% than 1 micron Coating  1% 1% 1%   1% Level Coating Stearic Stearic Stearic Stearic Type % CaCO₃  99% 99.2% 99.3%   90% % MgCO₃ 0.4% 0.3% 0.3% % SiO₂ 0.1% 0.02% 0.02% 0.15%

[0028] Compounding compositions 1 to 14 EX1 EX2 EX3 EX4 EX5 EX6 EX7 EX8 EX9 EX10 EX11 EX12 EX13 EX14 A 12 6 B 12 6 C 12 6 D 12 6 E 12 6 5 F (8102c) 12 F (8103C) 12 F (8101C) 12 6

[0029] Test panels of about 0.070 inch thickness by 3.5 inch wide were extruded for QUV accelerated testing purposes and exposed to QUV testing as follows.

[0030] QUV Weathering

[0031] QUV accelerated testing was under UVA 340 lamp, 50 degrees C., with 4 hours condensation. Measurements are in Hunter Delta B. EX1 EX2 EX3 EX4 EX5 EX6 EX7 EX8 EX9 EX10 EX11 EX12 EX13 EX14   350 HRS −0.32 0.08 0.02 −0.06 −0.43 −0.42 −0.61 −0.34 −0.17 −0.13 −0.15 −0.12 0.53 0.33   700 HRS −0.19 0.32 0.47 0.23 −0.34 −0.19 −0.56 −0.03 0.37 0.6 0.96 1.35 1,050 HRS 0.5 1.18 1.29 1.82 0.74 1 −0.38 0.24 1.09 1.17 2.16 2.6 1,500 HRS 2.05 2.72 3.98 3.37 0.83 2.01 0.07 0.66 1.63 2.18 1.65 2.24  2000 HRS 2.57 3.18 2.04 3.02 2.29 2.65 1.26 2.57 1.01 1.75

[0032] While in accordance with the Patent Statutes the best mode and preferred embodiments have been set forth, the scope of the invention is not intended to be limited thereto, but rather only by the scope of the attached claims 

What is claimed is:
 1. A weather resistant polyvinyl chloride (PVC) resin compounding composition, comprising: a rigid PVC resin; and at least about 2 weight parts of non-precipitated, sedimentary Caribbean calcium carbonate per 100 weight parts of PVC resin, the calcium carbonate having a particle size less than about 10 microns and is about 98% or more by weight pure calcium carbonate essentially free of iron.
 2. The rigid PVC compounding composition of claim 1, wherein the Caribbean calcium carbonate particle size is less than about 6 microns.
 3. The rigid PVC compounding composition of claim 1, wherein the particle size of the Caribbean calcium carbonate is less than about 3 microns.
 4. The rigid PVC compounding composition of claim 1 , wherein the particle size of the Caribbean calcium carbonate comprises from about 1 to about 3 microns or lower.
 5. The rigid PVC compounding composition of claim 1, wherein the Caribbean calcium carbonate contains impurities by weight are less than about 1% magnesium carbonate, less than about 0.3% acid insolubles, and less than about 0.1% silica.
 6. The rigid PVC compounding composition of claim 1, wherein the calcium carbonate is Jamaican calcium carbonate.
 7. The rigid PVC compounding composition of claim 1, containing from about 2 to about 50 weight parts of Caribbean calcium carbonate.
 8. The rigid PVC compounding composition of claim 2, containing from about 5 to about 15 weight parts of Jamaican calcium carbonate.
 9. The rigid PVC compounding composition of claim 1, wherein the Caribbean calcium carbonate is wet ground calcium carbonate.
 10. The rigid PVC compounding composition of claim 1, wherein the Caribbean calcium carbonate is dry ground calcium carbonate.
 11. The rigid PVC compounding composition of claim 1, wherein the micritic calcium carbonate particles are surface treated with a stearate.
 12. The rigid PVC compounding composition of claim 1, containing at least about 0.5 weight part s of organotin stabilizer based on 100 weight parts of PVC.
 13. The rigid PVC compounding composition of claim 2, containing from about 0.5 to about 3 weight parts of organotin stabilizer.
 14. The rigid PVC compounding composition of claim 6, containing from about 1 to about 2 weight parts of organotin stabilizer.
 15. The rigid PVC compounding composition of claim 12, wherein the organotin stabilizer comprises substituted mono-alkyl or dialkyl or trialkyl esters of tin with mono-, di-, or tri-substituted active mercapto groups or carboxylate groups.
 16. The rigid PVC compounding composition of claim 15, wherein the organotin stabilizer comprises mercapto groups.
 17. The rigid PVC compounding composition of claim 12, wherein the organotin stabilizer comprises a dialkyl mercapto compound.
 18. The PVC compounding composition of claim 13, wherein the organotin stabilizer comprises dialkyl ester mercaptide.
 19. The PVC compounding composition of claim 13, wherein the organotin stabilizer comprises dibutyl tin mercaptide.
 20. The rigid PVC compounding composition of claim 8, wherein the organotin stabilizer comprises dibutyl tin ethyl hexyl mercaptoacetate.
 21. The PVC compounding composition of claim 15, wherein the organotin stabilizer comprises active carboxylate groups.
 22. The PVC compounding composition of claim 21, wherein the carboxylate group comprises carboxylic acid.
 23. The rigid PVC compounding composition of claim 21, wherein the carboxylate group comprises an ester of carboxylic acid.
 24. The rigid PVC compounding composition of claim 12, containing at least about 0.1 weight parts of zinc dialkyl ester scavenger per 100 weight parts of PVC resin.
 25. The rigid PVC compounding composition of claim 15, containing at least about 0.1 weight parts of zinc dialkyl ester scavenger per 100 weight parts of PVC resin, provided the equivalents of active mercapto groups or carboxylate groups in the organotin are equal to or exceed the equivalents of dialkyl ester groups in the zinc dialkyl ester.
 26. The rigid PVC compounding composition of claim 20, containing from about 0.1 to about 2 weight parts of zinc dialkyl ester.
 27. The rigid PVC compounding composition of claim 1, wherein the PVC resin is essentially a homopolymer.
 28. The rigid PVC compounding composition of claim 1, wherein the PVC comprises a copolymer of copolymerized vinyl chloride monomer with less than 5% by weight copolymerized other unsaturated co-monomer.
 29. The rigid PVC compounding composition of claim 28, wherein the other unsaturated co-monomer is a vinyl monomer.
 30. The rigid PVC compounding composition of claim 28, wherein the other unsaturated co-monomer is a mono-ethylenically unsaturated monomer.
 31. A weather resistant polyvinyl chloride (PVC) compounding composition, comprising: a rigid PVC resin; at least about 2 weight parts of a non-precipitated, finely divided, chalk calcium carbonate having a particle size less than about 10 microns and at least about 98% pure calcium carbonate essentially free of iron; at least about 0.5 weight parts of an alkyl substituted organotin having one, two, or three non-alkyl substituted active mercapto or carboxylate groups; at least about 0.1 weight parts of zinc dialkyl ester scavenger, where the equivalents of zinc alkyl groups is less than the equivalents of non-alkyl active mercapto or carboxyl groups of the organotin; and where all weight parts are based on 100 weight parts of PVC resin.
 32. The rigid PVC resin compounding composition of claim 31, containing from about 2 to about 50 weight parts of said calcium carbonate.
 33. The rigid PVC resin compounding composition of claim 32, containing from about 0.5 to about 3 weight parts of said organotin.
 34. The rigid PVC compounding composition of claim 33, wherein the organotin comprises a mercapto compound.
 35. The rigid compounding composition of claim 33, wherein the organotin comprises a carboxylate compound.
 36. The rigid PVC compounding composition of claim 33, containing from about 0.1 to about 2 weight parts of said zinc dialkyl ester.
 37. A process for producing a rigid polyvinyl chloride (PVC) resin compounding composition, the process comprising: providing a non-precipitated, sedimentary Caribbean micritic calcium carbonate having a particle size less than about 10 microns, at least about 98% pure calcium carbonate, and essentially free of iron; and mixing the calcium carbonate with PVC resin to form a PVC compounding composition containing at least about 2 weight parts calcium carbonate per 100 weight parts of PVC resin.
 38. The process of claim 37, wherein the compounded PVC resin and micritic calcium carbonate are mixed with at least about 0.5 weight parts of organotin stabilizer based on 100 weight parts of PVC resin.
 39. The process of claim 38, wherein the Caribbean calcium carbonate is wet or dry ground to provide a particle size less than about 6 microns.
 40. The process of claim 39, wherein the Caribbean calcium carbonate is wet ground to provide the particle size.
 41. The process of claim 39, wherein the Caribbean calcium carbonate is dry ground to provide the particle size.
 42. The process of claim 37, wherein the PVC compounding composition is formed into a rigid PVC article.
 43. The process of claim 37, wherein the PVC compounding composition is extruded into a rigid PVC article.
 44. The process of claim 37, wherein the PVC compounding composition is molded into a rigid PVC article.
 45. A rigid PVC article comprising the composition of claim
 1. 46. A rigid PVC article comprising the composition of claim
 8. 47. A rigid PVC article comprising the composition of claim
 12. 48. A rigid PVC article comprising the composition of claim
 20. 